The human spine includes individual vertebras that are connected to each other. Under normal circumstances the structures that make up the spine function to protect the neural structures and to allow us to stand erect, bear axial loads, and be flexible for bending and rotation. However, disorders of the spine occur when one or more of these spine structures are abnormal. In these pathologic circumstances, surgery may be tried to restore the spine to normal and to relieve the patient of pain. The goal of spine surgery for a multitude of spinal disorders is often filling of voids within a pathologic vertebral body (exemplified by kyphoplasty or vertebroplasty procedures), replacement of a degenerated intervertebral disc with an intervertebral implant device that preserves mobility (disc replacement) or one that fuses adjacent vertebral segments (interbody and posterolateral fusions). Fusion works well because it stops pain due to movement at the facet joints or intervertebral discs, holds the spine in place after correcting deformity, and prevents instability and or deformity of the spine after spine procedures such as laminectomies or verterbrectomies. However, maintaining spinal mobility between the intervertebral discs and facets may be preferred over fusion in some cases to allow more flexibility of the spine and to decrease the risk of problems above and below the level of the fixation due to increased stress at the adjacent moveable segments.
The common approach to the removal of diseased intervertebral discs or vertebras includes a posterior laminectomy to first decompress the posterior neural elements and to gain access either through a direct posterior approach, or through a transpedicular approach, or through a posterior-lateral or transforaminal approach. After posterior exposure, the intervertebral discs can be removed and replaced with an interbody fusion device inserted through a posterior-lateral approach (PLIF-Posterolateral interbody fusion) or through a lateral transforaminal approach (TLIF/T-PLIF-Transforaminal lateral interbody fusion). Although open laminectomy provides exposure of the disc space, the large size of current interbody devices often makes it technically challenging to avoid injury to the dura and nerve roots during insertion of interbody devices. The large exposure also puts the neural elements and spinal cord at risk from direct mechanical injury during insertion or scarring from overlying soft tissues postoperatively. Scarring is considered a major cause for failed back syndrome in which patients continue to have back and leg pain after spinal surgery. In order to avoid neural injuries with posterior interbody fusion devices some surgeons elect to approach the spine anteriorly, which allows for direct removal of intervertebral discs and vertebras without exposing the neural tissues. Vertebral bodies and intervertebral discs can also be removed anteriorly through a peritoneal or retro-peritoneal approach. Anterior approaches are now more popular and are becoming the standard approach for implanting intervertebral disc replacement or interbody fusion (ALIF-Anterior lumbar interbody fusion) devices but still require major surgery and in cases of interbody fusion they require a second open posterior exposure for supplemental postero-lateral instrumented fusion and harvesting of iliac crest bone graft.
Thus, there is increasing consensus among surgeons that there is a need to develop devices, instruments, and methods to limit the size of the incision, extensive muscle stripping, prolonged retraction of muscles for visualization, avoidance of neural tissue retraction and injury, and denervation and devascularization that are known to contribute to poorer patient outcome after traditional open surgeries to treat pathologies deep within the body. In many cases these complications lead to permanent scarring and pain that can be more severe than the pain from the initial ailment. Limiting these complications in addition to the operative, general anesthesia, and recovery times are among the goals of this invention and that of percutaneous or minimally invasive surgeries.
Current disc replacement and interbody fusion devices are fixed in size and shape and although techniques are now being developed to insert these devices percutaneously, for example U.S. Pat. Nos. 5,792,044 and 5,902,231 attributed to Foley et al., the fixed size and shapes of these interbody devices still require distraction instrumentation and techniques to access the intervertebral disc space which necessitates open surgery for anterior placements and limited open exposures for posterior procedures. Although the focus is shifting away from fusion towards maintaining motion with facet replacements and an interbody device (disc or vertebral body replacements), the majority of these disc replacement devices are designed based on a ball-and-socket articulating principle with variable degrees of motion in different planes from a constrained device limiting some motion to a fully unconstrained device with motion in all planes. However, these devices do not permit percutaneous access primarily because they are fixed in shape and size, need to be inserted as separate articulating components, require distraction instrumentation and techniques to open the disc space, and they need to be anchored to the vertebral endplate.
Accordingly, there is a need for an intervertebral implant device that can be inserted in a collapsed state via minimally invasive surgery (MIS) and then can be expanded in situ distally.